Low tire pressure alarm system for pneumatic tires

Abstract

A low tire pressure alarm system for pneumatic tires, wherein a radio transmitter which is adapted to produce an alarm signal of a predetermined frequency upon detection of an abnormal pressure drop is accommodated in a hollow casing for mounting on a wheel cap casing of a vehicle wheel. The alarm signal is transmitted through the hollow casing per se or through a metal coating on the hollow casing where the latter is formed from a non-conductive material. The transmitted signal is received by a receiving set which includes a receiving antenna located on the underside of the vehicle body for shielding the same from spurious or extraneous signals and a radio receiving unit mounted within a luggage compartment of signals. Upon reception of the alarm signal, the radio receiver actuates an alarming device which produces a flashing light or sound to indicate the pressure drop to an operator of the vehicle.

What is claimed is: 
     
       1. A low tire pressure alarm system for a pneumatic tire on a vehicle wheel including a wheel disc, a rim securely mounted on said wheel disc and having flanges for holding said tire, and a wheel cap casing covering an outer side of said wheel, said alarm system comprising in combination: a low tire pressure detector in pneumatic communication with the interior of said tire for detection of a tire pressure drop below a predetermined level;   a hollow casing of a non-conductive material securely mounted on and substantially at the center of said wheel cap casing of said vehicle wheel:   a radio transmitter accommodated in said hollow casing and including a transmitting antenna in insulated relation with said wheel disc of said vehicle wheel and an oscillator having a resonance circuit electrically connected to said transmitting antenna and said wheel disc for producing an alarm signal of a predetermined frequency between said transmitting antenna and said wheel disc upon detection of an abnormal tire pressure drop by said detector; and   a receiving set including a receiving antenna mounted on the underside of a vehicle body for reception of an alarm signal transmitted from said radio transmitter and a radio receiver unit connected to said receiving antenna for actuating alarm means in response to said alarm signal.   
     
     
       2. A low tire pressure alarm system as defined in claim 1, wherein said radio transmitter has a transmitting antenna located outwardly of said flange of said rim. 
     
     
       3. A low tire pressure alarm system as defined in claim 1, wherein said low tire pressure detector is connected to a valve stem of said tire. 
     
     
       4. A low tire pressure alarm system as defined in claim 3, further comprising a power source in the form of a battery accommodated in said hollow casing and connected to said low tire pressure detector and said radio transmitter for energizing said transmitter upon detection of an abnormal pressure by said detector. 
     
     
       5. A low tire pressure alarm system as defined in claim 1, wherein said wheel cap casing is formed from a non-conductive and said hollow casing is adapted to serve as a transmitting antenna for said radio transmitter. 
     
     
       6. A low tire pressure alarm system as defined in claim 5, wherein said hollow casing serving as a transmitting antenna is mounted on the other side of said wheel cap casing. 
     
     
       7. A low tire pressure alarm system as defined in claim 5, wherein said hollow casing serving as a transmitting antenna is mounted on the inner side of said wheel cap casing. 
     
     
       8. A low tire pressure alarm system as defined in claim 1, wherein said radio receiver unit is mounted within a luggage compartment of the vehicle. 
     
     
       9. A low tire pressure alarm system as defined in claim 1, wherein said low tire pressure detector is mounted on said wheel cap casing of said vehicle wheel and connected to a valve stem of said tire by way of a tubing. 
     
     
       10. A low tire pressure alarm system as defined in claim 1, wherein said hollow casing is formed from a non-conducting material and provided with a metal coating serving as a transitting antenna for said radio transmitter. 
     
     
       11. A low tire pressure alarm system for a pneumatic tire on a vehicle wheel including a wheel disc, a rim securely mounted on said wheel disc and having flanges for holding said tire, and a wheel cap casing convering an outer side of said wheel, said alarm system comprising in combination: a low tire pressure detector in pneumatic communication with the interior of said tire for detection of a tire pressure drop below a predetermined level;   a hollow casing of non-conductive material securely mounted on and substantially at the center of said wheel cap casing of said vehicle wheel;   a radio transmitter accommodated in said hollow casing and connected to said low tire pressure detector for producing an alarm signal of predetermined frequency upon detection of an abnormal tire pressure drop by said detector; and   a receiving set including a receiving antenna for reception of an alarm signal transmitted from said radio transmitter and a radio receiver unit connected to said receiving antenna for actuating alarm means in response to said alarm signal; said hollow casing being formed from a non-conducting material and provided with a metal coating serving as a transmitting antenna for said radio transmitter; said hollow casing having a truncated cone shape and having its diverging end securely fitted into an annular groove formed in the center portion of said wheel cap casing concentrically with respect to a center aperture thereof and said radio transmitter is mounted on an insulating plate covering said center aperture on the outer side of said wheel cap casing and clamped tightly to said hollow casing together with a backing plate covering said center aperture on the inner side of said wheel cap casing.   
     
     
       12. A low tire pressure alarm system as defined in claim 10, wherein said metal coating is provided on both the outer and inner wall surfaces of said hollow casing. 
     
     
       13. A low tire pressure alarm system as defined in claim 10, wherein said metal coating is provided on the outer wall surface of said hollow casing. 
     
     
       14. A low tire pressure alarm system as defined in claim 10, wherein said metal is provided on the inner wall surface of said hollow casing. 
     
     
       15. A low tire pressure alarm system as defined in claim 1, wherein said radio transmitter is provided with a wire coil antenna for transmission of said alarm signal.